The invention relates to improvements in treatment of sewage effluent to raise the quality of waste water produced in sewage disposal systems, e.g., septic tanks, aerobic treatment or settling pond systems. It appertains particularly to the removal of phosphates by a filter bed which receives untreated or partially treated sewage from a system operating aerobically or anaerobically for stabilization of the waste.
In today's concern for the protection of human health and the natural environment, populous areas are generally equipped with sewage treatment facilities of some kind to destroy dangerous bacteria or viruses and remove unwanted contamination and nutrients that would pollute the surface or ground water.
In parts of the country not served by a municipal sewage treatment plant, in farmland and recreational areas, the septic tank system is considered satisfactory so that its use continues to increase. In the conventional septic tank system, it is normal practice to lay the drainage pipes or tiles for distribution of sewage in a trench, twenty-four to thirty-six inches deep and about eighteen to thirty-six inches wide with the total length of the distribution system determined by the volume of the daily sewage discharge and the absorptive capacity of the soil.
In septic tank sewage treatment systems, the leaching bed should have a depth of at least 40 inches of soil below the drainage pipe or tiles and the underground water, bedrock or any impervious strata should be at least five feet below ground surface. Where the leaching bed cannot operate effectively due to the water table being high, soil characteristics for the absorption poor, or soil cover over rocks is thin, sewage effluent in only insufficiently treated condition reaches the water table to contaminate it with pathogens, undesirable pollutants and nutrients such as phosphates, ammonia, etc.
In areas where conventional subsurface waste disposal systems cannot be installed due to the aforementioned reasons, alternate and better methods for the treatment of sewage are required. Accordingly, it is an object of this invention to provide an improved method of treating sewage to remove the noxious pollutants such as organic matter, contaminants containing nutrients such as phosphates nitrogen, pathogens, viruses, etc., in a leaching bed provided with chemical additives.
A further object of the invention is to provide a filter layer for a sewage leaching bed in which the filter includes a layer of soil with chemical additives that resist being washed out by adhering to the soil by physio-chemical bonds.
To the accomplishment of these and related objects, the invention resides in the sewage treatment method and the filter or leaching bed construction hereinafter more fully described, illustrated in the accompanying drawings and pointed out in the claims hereunto appended.